Problem scenario
You are using a Debian distribution of Linux, and there is a .gpg file in your .../trusted.gpg.d/ directory that you want eliminated. What should you do?
Solution
1. Run this: sudo apt-key list
2. Mentally identify the matching key you want deleted. Here is an example of the output from the above command:
/etc/apt/trusted.gpg.d/cccv-archive-key.gpg
-------------------------------------------
pub rsa3072 2021-08-14 [SC] [expired: 2022-04-24]
1234 ABCD 5678 EFGH 9101 IJKL 1112 MNOP 1314 QRST
uid [ expired] packages.cccv.de <infra@cccv.de>The alphanumeric string you need is after the "[expired: 2022-04-24] section and before the "uid" string.
3. Run this command with the string obtained in step #2: sudo apt-key del "1234 ABCD 5678 EFGH 9101 IJKL 1112 MNOP 1314 QRST"